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Vitamin D3 illustration

Vitamin D3

An essential nutrient most adults are insufficient in. Strong bone-health and deficiency-correction evidence; mood claims weak in non-deficient adults per VITAL-DEP.

Essentials Last verified 2026-05-06
stress and mood energy

What it does

Vitamin D3 (cholecalciferol) at 1000 to 4000 IU daily is sufficient for most adults to reach the 30 to 50 ng/mL serum range associated with reduced disease risk. K2 (MK-7) co-supplementation rationale is strongest for postmenopausal and older adults.

  • Bone health and fracture prevention Strong evidence

    Increases intestinal calcium absorption; with adequate calcium, supports bone mineral density and reduces fracture risk in deficient older adults.

    Sources: PMID 21646368 · NIH ODS Vitamin D Health Professional Fact Sheet

  • Immune function (respiratory infections) Moderate evidence

    Modulates innate and adaptive immunity. The 2021 IPD meta-analysis found supplementation modestly reduced acute respiratory infections.

    Sources: PMID 33798465

  • Mood / depression (limited; deficiency-only) Preliminary evidence

    VITAL-DEP (n=18,353, 2000 IU/day, 5.3 years) found NO benefit for depression incidence or recurrence in mostly-replete adults >=50. Possible benefit only when correcting frank deficiency.

    Sources: PMID 32749491

Top picks

  1. 1

    Thorne

    Vitamin D/K2 Liquid

    Liquid drops; clean ingredients; D3 + K2.

    Check on Amazon
  2. 2

    NOW Foods

    Vitamin D-3 + K-2 (1000 IU / 45 mcg)

    Veg capsules; lower dose for those nearer the RDA.

    Check on Amazon
  3. 3

    Sports Research

    Vitamin D3 + K2 Softgels (5000 IU + 100 mcg MK-7)

    Higher dose; oil-based softgel.

    Check on Amazon

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How to use it

Dosage
1000 to 4000 IU/day (RDA 600 to 800 IU; UL 4000 IU). 2000 IU/day brings most adults to >=30 ng/mL.
Timing
Once daily, morning or with the largest meal.
With food
Yes
Onset
Serum 25(OH)D plateaus in 8 to 12 weeks; retest at 3 months.

What to look for

  • D3 (cholecalciferol) over D2 (D3 raises and sustains 25(OH)D more effectively per Tripkovic 2012).
  • K2 as MK-7 (long half-life) over MK-4 if co-supplementing; rationale strongest for postmenopausal and older adults.
  • Oil-based softgel (fat-soluble; superior bioavailability vs dry tablets).
  • Third-party tested (USP, NSF, ConsumerLab) - D3 potency is commonly mislabeled.
  • Per-serving dose 1000 to 5000 IU; avoid mega-doses unless clinician-directed.

Formats: softgels, drops.

Skip if:
  • Hypercalcemia.
  • Sarcoidosis or other granulomatous disease (extrarenal calcitriol overproduction).
  • Hyperparathyroidism or kidney stones (clinician supervision required).
  • Concurrent thiazide diuretics or digoxin (additive hypercalcemia / arrhythmia risk).

FAQ

Do I really need to test?
Recommended once before starting and again after 3 months. Sun exposure, latitude, and skin tone produce huge interindividual variation in baseline serum levels.

Related comparisons

Additional references